Gymnocalycium horstii Buining
Gymnocalycium horstii subsp. horstii
The native range of this species is from southern Brazil, eastern Paraguay, northeastern Argentina, to Uruguay. It occurs on rocky outcrops at elevations up to 980 feet (300 m).
Gymnocalycium horstii is a cactus with green depressed globose stems with 5 to 6 ribs, each with 3 to 5 woolly areoles, out of which grow spines curved back towards the body. The stems grow up to 10 inches (25 cm) in diameter, usually producing offsets to form a clump over time. Each areole usually bears 5, rarely 6, yellowish-white to pale yellow, up to 1.2 inches (3 cm) long spines. Flowers vary in color from white to pale pink. They are funnel-shaped, up to up to 4 inches (10 cm) long, nearly equal in diameter, and appear in spring. Fruits are ovoid, bluish-green when ripe, and 2.4 inches (6 cm) long.
The specific epithet "horstii (HORST-ee-eye)" honors Leopoldo Horst (1918-1987), a German-born Brazilian cactus collector and exporter in Rio Grande do Sul.
USDA hardiness zones 10a to 11b: from 30 °F (−1.1 °C) to 50 °F (+10 °C).
How to Grow and Care
Some Gymnocalyciums are shade-seeking in the wild, among shrubs or grasses, while others grow completely exposed. Therefore, some will need light shading from the sun in the hottest months, but to overdo this will result in the loss of flowers.
The potting medium's balance should be sufficient to allow good drainage so that the plants do not sit in soggy soil for more than a day or two after watering.
Watering in the summer months, while the plants are growing well, can be frequent (weekly for small plants in small pots), but always allow the compost to dry out before rewatering. Watering in the winter months is unwise and certainly not necessary. The difficult times are spring and autumn.
Those species which produce offsets can be readily propagated by cuttings. Gymnocalycium seed germinates well when fresh and will keep for a few years if stored in cold conditions.
See more at How to Grow and Care for Gymnocalycium.
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